Roof covering

Abstract

A roof covering suitable for use on flat or shallow angle roofs is of sheet-like form and has at least one raised region (7) in the sheet, the raised region (7) merging into undulations (5) of the border (2) surrounding the raised region (7). The shape of the covering enables differential expansion and or contraction effects between the covering and a substrate (3) on which it is laid to be accommodated.

I claim: 
     
       1. A roof covering suitable for use on flat or shallow angle roofs, the covering being in the form of a sheet having means for accommodating substantial expansion and contraction of the sheet along its plane dimensions, said means comprising at least one preformed raised deformable intermediate region of the sheet having a predetermined subtended volume and merging curvedly downwardly over upwardly convex surface portions of the sheet directly into pluralities of preformed smooth deformable undulations surrounding the raised region, with each undulation being of subtended volume small compared with said predetermined volume of the raised region, and with the lower points of at least some of the undulations being arranged to rest upon and to be secured to a substantially planar roof substrate. 
     
     
       2. A covering as claimed in claim 1 in which the raised region is of essentially inverted-dish shape. 
     
     
       3. A covering as claimed in claim 1, wherein said expansion and contraction accommodating means includes a plurality of said preformed raised regions each merging into corresponding surrounding pluralities of preformed smooth deformable undulations as aforesaid. 
     
     
       4. A covering as claimed in claim 1, wherein the raised region and the undulations are dimensioned such that a uniform flattening of their shapes will occur when stretching forces are applied at edges of the sheet. 
     
     
       5. A covering as claimed in claim 1, in which the length of each undulation is within the range of from 15 mm to 600 mm. 
     
     
       6. A covering as claimed in claim 1, in which the height of each undulation, at its highest point, is within the range of from 1 mm to 40 mm. 
     
     
       7. A covering as claimed in claim 1, in which the height of each raised region, at its highest point, is not less than 10 mm. 
     
     
       8. A covering as claimed in claim 1, in which the sheet is made from plastic. 
     
     
       9. A covering as claimed in claim 8, in which the plastic comprises at least one substance selected from the group consisting of polyesters, epoxy/amines, epoxy/polyamides, phenolics, vinylated polymers, polystyrenes, nylons, styrene copolymers, acrylic polymers, acrylic copolymers, polyurethanes, polyethylenes and polypropylenes. 
     
     
       10. A covering as claimed in claim 8, in which the plastic incorporates reinforcement. 
     
     
       11. A covering as claimed in claim 10, in which the reinforcement comprises one of fibers and strands. 
     
     
       12. A covering as claimed in claim 10, in which the reinforcement includes reinforcement selected from the group consisting of chopped fibers, chopped strands, twisted strand material, and woven strand material. 
     
     
       13. A covering as claimed in claim 10, in which the reinforcement includes a material selected from the group consisting of glass, metal, carbon and plastics. 
     
     
       14. A covering as claimed in claim 13, in which the plastics are selected from the group consisting of polyesters, nylons, acrylics, polyethylenes and polypropylenes. 
     
     
       15. A covering as claimed in claim 1, in which the sheet is formed from one of metal and wood. 
     
     
       16. A covering as claimed in claim 1, in which the lower points of the undulations are located in a common plane. 
     
     
       17. A covering as claimed in claim 1, the sheet being in the form of a panel. 
     
     
       18. A roof structure comprising a plurality of sheets according to claim 1 arranged side-by-side and each having the lower points of at least some of its undulations secured to the substrate. 
     
     
       19. A roof structure as claimed in claim 18, wherein the undulations of adjacent panels are aligned. 
     
     
       20. A method of smoothly accommodating for differential thermal expansion and contraction effects between a substantially planar roof substrate and a sheet-like covering secured thereto, comprising the steps of providing a sheet having at least one preformed raised deformable intermediate region of predetermined subtended volume and merging smoothly curvedly downwardly over upwardly convex surface portions of the sheet directly into surrounding pluralities of preformed smooth deformable undulations each of subtended volume small compared with said predetermined volume; placing the sheet on the substrate such that the lower points of the undulations lie in the plane of the substrate; and securing the lower points of at least some of the undulations to the substrate, such that the raised region and surrounding undulations may deform to accommodate differential thermal expansion and contraction effects between the sheet and the substrate along the plane dimensions of the sheet.